Method of constructing an insulating device



L. E. SAUER 3,484,938

INSULATING DEVICE Dec. 23, 1969 METHOD OF CONSTRUCTING AN 5 Sheets-Sheet 1 Filed May 11, 1966 INVENTOR Louis E. Scuer ATTNEY WITNESSES Dec. 23, 1969 Dec. 23, 1969 l L. E. SAUER METHOD OF CONSTRUCTING AN INSULATING DEVICE 3 Sheets-Sheet 5 FIGLT.

FIGS.

United States Patent 3,484,938 METHOD OF CONSTRUCTING AN INSULATING DEVICE Louis E. Sauer, Sharon, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Continuation-impart of application Ser. No. 104,339,

Apr. 20, 1961. This application May 11, 1966, Ser.

Int. Cl. H01b 19/00 US. Cl. 29-631 Claims ABSTRACT OF THE DISCLOSURE An electrical insulator especially suitable for use in a condenser bushing is formed of a resilient strip of insulating material having at least one shed extending from one surface thereof and having a keyway extending along one shed extending from one surface thereof and having a keyway extending along one surface near one edge and a key extending along the other surface near the other edge whereby adjacent turns are interlocked with each other and a spiral shed is formed which extends along the length of the insulating structure. Additionally, the strip has progressive changes in the thickness thereof at spaced intervals to accommodate the progressively changed diameters of the conductive cylinders of a condenser bushing.

This application is a continuation-in-part of copending application Ser. No. 104,339, filed Apr. 20, 1961, by Louis E. Sauer for Self-Cleaning Electrical Insulator Constructions now issued Patent 3,257,501 and assigned to the assignee of the instant invention.

In the aforementioned copending application, a bushing or a standoff insulator constructed according to my invention or discovery has helicoidal sheds; I have discovered and disclosed that there is a critical range of average circumferential pitch, defined as the ratio of lead to the root circumferential distance for a constant lead, which gives optimum flashover characteristics, ratios within this critical range providing a desired slope to the shed surfaces so that substantial dripping over the edge of the shed surfaces does not occur, while at the same time the slope of the shed surfaces is not sufiiciently great so that the water flow becomes so thin that the current carrying capacity of the water decreases and as a result arcing occurs at a lower voltage. In the aforementioned copending application the discovery was applied to bushings having internal stepped lands for supporting condenser tubes to form a condenser bushing, and was also applied to standoff and suspension type insulator devices.

In summary. the method of my invention may be ap plied to the construction of a weather casing for a condenser bushing, or may be applied to the construction of a standoff or post type insulator, or the construction of a stud type bushing, or a modified post type insulator, and includes the step of wrapping successive turns of a keyed strip or keyed strips of resilient insulating material around a molding form, each strip of insulating material having at least one ridge extending therefrom to provide a shed-forming surface, the resulting product being a weather casing or an insulator having at least one helical shed, and if desired more than one helical shed, with the turns of the insulating material interlocking each other.

Accordingly, a primary object of my invention is to provide a new and improved method of constructing an insulator device.

Another object is to provide a new and improved method of constructing a standoff insulator.

A further object is to provide a new and improved 3,484,938 Patented Dec. 23, 1969 method of constructing a weather casing for a condenser bushing.

Still a further object is to provide a new and improved method of constructing a stud type bushing.

These and other objects will become more clearly apparent after a study of the following specification, when read in connection with the accompanying drawings, in which:

FIGURE 1 illustrates a post type insulator which may be constructed by the method of my invention;

FIG. 2 illustrates a weather casing for a condenser bushing which may be constructed according to the method of my invention;

FIG. 3 is a partial sectional view of a suspension insulator constructed according to the method of my invention;

FIG. 4 illustrates a sectional view in a vertical plane taken through a standoff or post type insulator which may be constructed by the method of my invention;

FIG. 5 illustrates a stud type bushing which may be constructed by the method of my invention;

FIG. 6 is a plan view of the weather casing or rubberlike weather shell of FIG. 2;

FIG. 7 is a sectional view taken substantially along the line VII-VII of FIG. 2;

FIG. 8 shows in more detail my method, in which a keyed strip of insulating material having a shed formed thereon is continuously wrapped in a manner having interlocking turns so as to form a weather casing or insulator with at least one helical shed; and

FIG. 9 illustrates the method of my invention in which the keyed strip is somewhat wider than the strip of FIG. 8, and a number of parallel spaced sheds are formed on the strip so that each turn of the strip as it is wrapped to form the weather casing supplies a plurality of sheds, or a plurality of revolutions of the same shed.

Referring now to the drawings for a more detailed understanding of the invention, and in particular to FIG. 1 thereof, a post type insulator is generally designated 11, having a threaded stud 12 extending from the top thereof, having a base 13, and being formed by winding a strip 15 of resilient insulating material, having a shed 16 formed therein, it being observed from FIG. 1 that a number of adjacent wound strips are employed so that several diiferent helical sheds 16, 17 and 18 are provided, on one strip having several sheds thereon, it being understood that if desired, a fourth shed which terminates at a position not illustrated in the drawing may also be provided.

Particular reference is made now to FIG. 2, Where a weather casting for a condenser bushing constructed according to my invention is shown, the interlocking features of the turns being omitted for simplicity of illustration, the weather casing being generally designated 21 and having on the hollow interior thereof a plurality of stepped lands, steps 22 and 23 of the lands being shown, the stepped lands being provided for conveniently receiving and supporting the concentric cylinders of conductive material and of graduated diameters of a condenser bushing, in a manner which will be readily understood by those skilled in the art. The weather casing 21 has a threaded upper end 25, and the slope of the sheds and number of sheds are chosen in accordance with the teachings of the aforementioned copending application Ser. No, 104,339 for Self-Cleaning Electrical Insulator Construction.

Particular reference is now made to FIG. 8 in which further details of the method of constructing the weather casing of FIG. 2 are shown. Strip generally designated 28 may be an' extruded non-tracking rubber strip having a cross-section as shown in the drawing, with an extended ridge or shed-forming portion 29; the thick portion of the strip 28 adjacent the shed portion 29 having a keyway 31 formed therein, into which extends the key or anchor 32 formed along the entire surface of the next adjacent turn underneath, so that, as will be seen, each turn of the strip of material as it is wrapped (if desired on a convenient form), interlocks around the entire perimeter of the turn with the turn immediately above, and also interlocks around the entire inner periphery of the turn with the turn immediately below, forming a weather casing which offers the same advantages which a casing cast in one piece would offer, but has the advantage of ease of construction by utilizing my aforedescribed method. Stepped lands 22' and 23' are also shown.

Particular reference is made now to FIG. 9, which shows an additional method of constructing the casing 21 with the stepped lands on the inside thereof, for use in the condenser bushing. In FIG. 9 a strip of resilient insulating material generally designated 35 has four sheds formed thereon, the sheds being designated 41, 42, 43 and 44, at spaced intervals along what will be the outside of the strip when the strip is wound to form a weather casing. The inside surface of the strip 35 has steps 38 and 39 therein. One edge of the strip 35 has an extended key 46 extending the entire length of the strip, the key 46 meshing with a keyway 47 formed in the adjacent strip or adjacent turn of the same strip, so the strip 35 interlocks with the adjacent strip or adjacent turn 36 on one side thereof. On the other side of the aforementioned strip 35, there is a keyway 50 which extends the entire length of the strip for receiving a key 49 attached to and forming part of the adjacent strip or adjacent turn 37 on that side, so that the strip 35 is locked around the entire periphery of the turn to adjacent strip or turn 36 above it and to adjacent strip or turn 37 below it. -It will be understood that strips identified separately for convenience of description may be adjacent turns of one strip; keys 46 and 49 may be portions of one key, and keyways 47 and 50 may be portions of one keyway. Cylindrical conductive members 52, 53 and 54 forming part of the condenser bushing are shown resting on the shoulders or lands 38, 39 and 40.

Particular reference is made now to FIG. 4. The outer shell or casing 57 of the standoff insulator having terminals 58 and 59 may be constructed by either of the aforedescribed methods described in connection with FIGS; 8 and 9, interlocking features of the turns not being shown for simplicity of illustration.

Particular reference is made now to FIG. 5, in which a stud type bushing is shown having a conductive stud 62, a main body of insulation 63, and a weather casing 64, the upper end of which fits snugly around a ground flange 66. The weather casing 64 may be formed by either of the methods described in connection with FIGS. 8 and 9.

Particular reference is made now to FIG. 3, illustrating an insulator which may be of the suspension type, having a steel ball bolt 71, a main body of insulation 72, and an outer shed or weather casing 73 which may be formed of a strip or strips of resilient insulating material, having a shed or sheds formed on the outer surface thereof and wrapped around the main insulating body 72, according to the methods of my invention.

Whereas I have described my methods of constructing an electrical insulating device, and illustrated certain types of electrical insulating devices which may be constructed according to my methods, it will be understood that the drawings and written description heretofore are illustrative and should not be interpreted in a limiting sense.

I claim as my invention:

1. The method of constructing a weather casing having at least one spiral shed for an electrical insulator which comprises the steps of forming a strip of resilient insulating material having formed on one surface thereof a shed and a key spaced therefrom, the shed and key extending substantially the length of the strip, and having a keyway formed in the opposite surface thereof at a position therein substantially immediately back of the shed and extending substantially the length of the strip, and wrapping the strip of insulating material to form a number of closely disposed turns with the key of one turn fitting into the keyway of an adjacent turn on one side thereof around the entire periphery of the said one turn, and the keyway of said one turn receiving the key of the next adjacent turn on the other side thereof around the entire periphery of said one turn, to form a weather casing having a body portion composed of insulating material and at least one outwardly extending spiral shed along the length thereof, the location of the keyway substantially back of the shed insuring that the thickness of the strip is not reduced to a value at which forces applied in Wrapping the strip would break the strip.

2. The method according to claim 1 of constructing a weather casing for a condenser bushing or such like device which comprises forming said strip of resilient electrically insulating material with one side of the strip having spaced shoulders or steps formed therein resulting from progressive changes in the thickness of the strip, the spaced steps being adapted to receive cylindrical conductive members of a condenser bushing.

3. The method of producing an electrical insulator having an extended body portion having at least two axiallyspaced spiral sheds extending the length thereof which comprises forming an extended strip of resilient electrically insulating material, the strip being generally rectangular in cross-section and having at least two spaced sheds extending from one surface thereof, the sheds being spaced at least a predetermined distance from the edges respectively of the strip, the strip having adjacent one surface thereof a portion of reduced thickness adjacent one edge with a key extending along the edge of the strip, the strip having adjacent the other surface thereof a portion of reduced thickness adjacent the other edge with a keyway extending along the length of the strip where the thickness is reduced, winding the strip in a plurality of closely spaced turns in a manner whereby the key of one turn fits into the keyway of an adjacent turn on one side, and the keyway of said one turn receives the key of an adjacent turn on the other side, to form an extended insulating structure having at least two spiral sheds extending the length thereof.

4. A method according to claim 3 wherein the strip is additionally characterized as having other progressive variations in the thickness thereof, the other progressive variations in thickness being of predetermined amounts and at distances from each other whereby the back surface of the strip is adapted to receive the cylindrical conductive layers of progressively increasing diameter of a condenser bushing.

5. The method according to claim 3 including the additional step of inserting a conductor stud through the electrical insulator.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 5/1958 Sweden.

JOHN F. CAMPBELL, Primary Examiner D. C. REILEY, Assistant Examiner US. Cl. X.R.

29-453; 161-47; l74-l8l, 184 

